1. Field
The present disclosure is directed to a method and apparatus for decoding a received message with a priori information. More particularly, the present disclosure is directed to decoding a message received on a control channel based on attributes from previous message streams.
2. Description of Related Art
Presently, wireless wide area networks can include Global System for Mobile communication (GSM) networks, Time Division Multiple Access (TDMA) networks, Code Division Multiple Access (CDMA) networks, cellular networks, and many other wireless wide area networks. These networks use traffic channels for transmitting and receiving data, such as voice data to and from a user using a mobile terminal, such as a cellular phone. These networks also use control channels for transmitting and receiving control signals. The control channels, which may be associated with a specific user traffic, or more generally may be mapped onto a dedicated physical layer resource, may typically be used to transfer control information from the network to a mobile terminal or to report measurement information from the mobile terminal to the network. For example, a GSM network can use a Slow Associated Control Channel (SACCH) to transmit control signals. The SACCH has a low bit rate, is associated uniquely with a specific mobile terminal, and is transmitted periodically with a relatively large time between transmissions. The SACCH can transmit specific control information and messages related to higher protocols, such as neighbor cell information, to a mobile terminal. A connection quality, such as a channel quality, of the mobile terminal with the network can be based on the signal quality of a control channel.
In some networks, including Global System for Mobile communication (GSM) networks, measures of control channel quality, including control channel bit or code block error rates, are often used to determine the fundamental quality of the communication link and to determine whether a link should be maintained or otherwise terminated on the basis of inadequate performance. Unfortunately, since the information transmission rate, modulation type, and error control coding methods applicable respectively to control channels and traffic channels may not be well matched, observation of control channel performance may not always be a useful guide to the performance of a companion traffic channel. For example, for a given ratio of desired signal to interfering signal plus noise ratio, the control channel bit or block error rate may significantly exceed that of an associated traffic channel. If, as in the case of the GSM traffic channel and associated control channel, the quality metric controlling maintenance of the radio channel is based on the control channel block error rate, the radio link may be terminated, either by the network or by the mobile station, even though the block error rate of the traffic channel meets the desired quality of service.
Thus, the channel quality of the control channel may not always accurately reflect the channel quality of a traffic channel. Therefore, if the control channel experiences poor channel quality, a link or call may be terminated, even though a mobile terminal is receiving a good traffic signal and the user is experiencing good communication.
Accordingly, there is a need for improving the decoding of a message received on a channel.